Fixed-time AI pregnancy rate following insemination with frozen-thawed or fresh-extended semen in progesterone supplemented CO-Synch protocol in beef cows
SummaryThe objective of this study was to compare fixed-time AI pregnancy rate in Angus crossbred beef cows inseminated with frozen-thawed or fresh-extended semen. Two ejaculates from each of two Angus bulls were collected by artificial vagina and pooled for each bull. The pooled semen from each bull was divided into two aliquots; Aliquot 1 was extended using Caprogen ® (LIC, Hamilton, New Zealand) to a concentration of 3 × 10 6 sperm/straw and Aliquot 2 was extended using egg-yolk-glycerol extender to a concentration of 20 × 10 6 sperm/straw.Semen extended with Caprogen ® was maintained at ambient temperature and semen extended with egg-yolk-glycerol extender was frozen and maintained at GnRH im and were inseminated at a fixed-time on Day 10, 66 h after CIDR removal. Timed-AI pregnancy rates were influenced by season (P < 0.05), cows detected in estrus prior to and at AI (P < 0.001), and dam age (P < 0.01).Pregnancy rates were not affected by semen type (Fresh = 51.5% vs. Frozen = 50.4%; P = 0.66) and there were no significant interactions of semen type by estrus expression, semen type by sire, or semen type by season (P > 0.1). In conclusion, commercial beef cows inseminated with fresh-extended semen (3 × 10 6 sperm/straw) yielded comparable pregnancy rates to conventional frozenthawed semen in a progesterone supplemented, CO-Synch fixed-time AI synchronization protocol and may provide an alternative to frozen semen for more efficient utilization of superior genetics.
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